Steering system of saddle-ride type vehicle

ABSTRACT

An assist motor generates a steering assist force that assists a steering force transmitted to a steering shaft. A steering assist force transmit member is turnably supported by steering stem, and an assist steering system link joins a steering arm and a steering assist force transmit member. The assist motor is disposed adjacent to an assist steering system link.

BACKGROUND

Field

The present invention relates to a steering system of a saddle-ride typevehicle.

Description of the Related Art

In the past, in a steering system of a saddle-ride type vehicle, therewas one disclosed in JP-A No. 2012-076490 (Patent Literature 1) forexample. In the steering system, a power assist unit that transmits asteering assist force to a steering shaft is provided, and an electricmotor of the power assist unit is attached to the bottom bridge side ofa head pipe through a support transmit member.

On the other hand, in a front wheel suspension device of a motorcycle,there is one disclosed in JP-A No. H4-169386 (Patent Literature 2) forexample. In the front wheel suspension device, a steering shaft link isarranged within a steering tube unit of a front fork that supports thefront wheel, and the upper and lower ends of the steering shaft linkprotruding to the outside of the steering tube unit are supported by abody frame through a swing arm that is arranged in a verticallyswingable manner.

In the meantime, in such front wheel suspension device, because it wasdifficult to incorporate an assist steering system that transmitted asteering assist force to a steering shaft while saving a space, therewas a problem that the steering system was enlarged.

SUMMARY

Therefore, an object of the present invention is to suppress enlargementof a steering system in the steering system of a saddle-ride typevehicle which includes a front fork that includes a steering shaft atthe upper end and supports a front wheel at the lower end, a steeringarm attached to the steering shaft, a steering force transmit memberthat is turnably supported by a steering stem that is arranged in a bodyframe, and a steering system link that joins the steering arm and thesteering force transmit member.

As a solution to the above-described problem, certain embodiments of theinvention include a steering system of a saddle-ride type vehicle,including a front fork that includes a steering shaft at the upper endand supports a front wheel at the lower end. A steering arm is attachedto the steering shaft, and a steering force transmit member that isturnably supported by a steering stem is arranged in a body frame. Asteering system link joins the steering arm and the steering forcetransmit member. An assist motor generates a steering assist force thatassists a steering force transmitted to the steering shaft, and asteering assist force transmit member is turnably supported by thesteering stem. An assist steering system link joins the steering arm andthe steering assist force transmit member are further provided. Theassist motor is disposed adjacent to the assist steering system link.

In certain embodiments, the assist motor is disposed between thesteering shaft and the steering stem in side view.

In certain embodiments, the body frame is connected to a rear end of aswing arm that extends vehicle forward and rearward and is madevertically swingable. A front end of the swing arm is connected to afork holder that steerably supports the front fork, and at least a partof the assist motor overlaps with the swing arm in side view.

In certain embodiments, the assist motor includes a motor body, and anoutput shaft that outputs rotational drive of the motor body as thesteering assist force. A steering assist force transmit mechanismtransmits the steering assist force outputted by the output shaft to thesteering shaft. The motor body is disposed downward of the steeringassist force transmit mechanism, and the output shaft is directedupward.

In certain embodiments, at least a part of the steering assist forcetransmit mechanism overlaps with the assist steering system link in sideview.

In certain embodiments, a stay supports vehicle components, and isattached to the body frame. The stay is provided with an assist motorsupport section that supports the assist motor.

Because in some embodiments the assist motor is disposed adjacent to theassist steering system link, a space adjacent to the assist steeringsystem link can be effectively utilized in disposing the assist motor.Therefore, enlargement of the steering system can be suppressed.

Because in some embodiments the assist motor is disposed between thesteering shaft and the steering stem in side view, the assist motorcomes to be positioned rearward of the front fork. Therefore, the assistmotor can be protected easily.

Because in some embodiments at least a part of the assist motor overlapswith the swing arm in side view, a space at the side of the swing armcan be effectively utilized in disposing the assist motor. Therefore,the assist motor can be disposed compactly.

Because in some embodiments the motor body is disposed downward of thesteering assist force transmit mechanism and the output shaft isdirected upward, compared to the case the motor body is disposed upwardof the steering assist force transmit mechanism and the output shaft isdirected downward, the motor body that is relatively heavy in the assistmotor can be disposed at a low position. Therefore, the position of thecenter of gravity of the vehicle can be lowered.

Because in some embodiments at least a part of the steering assist forcetransmit mechanism overlaps with the assist steering system link in sideview, a space at the side of the assist steering system link can beeffectively utilized in disposing the steering assist force transmitmechanism. Therefore, the steering assist force transmit mechanism canbe disposed compactly.

Because in some embodiments the assist motor support section thatsupports the assist motor is arranged in the stay, compared to the casea support member for supporting the assist motor is arranged separatelyand independently, the number of pieces of components can be suppressed.Also, compared to the case the assist motor is not supported, thevibration of the assist motor can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a left side view of the vehicle body front part of amotorcycle in an embodiment of the present invention.

FIG. 2 is a left side view of the steering system of the motorcycle.

FIG. 3 is a left side view of the periphery of a linkage link of thesteering system.

FIG. 4 is a left side view showing the steering system along with astay.

FIG. 5 is a drawing of the steering system as viewed from a directionalong the steering stem.

FIG. 6 is a drawing when a power assist unit of the steering system isviewed from a direction along the steering stem.

DETAILED DESCRIPTION

Embodiments according to the present invention will be described belowwith reference to the drawings. Also, the direction such as front, rear,left, and right in the description below shall be with reference to thedirection in the vehicle described below unless otherwise stated.Further, in the right place in the drawing, used in the descriptionbelow, there are shown an arrow FR denoting vehicle forward, an arrow LHdenoting vehicle left hand, an arrow UP denoting vehicle upward, and avehicle left-and-right center line CL.

FIG. 1 shows the vehicle body front part of a motorcycle as an exampleof a saddle-ride type vehicle. With reference to FIG. 1 and FIG. 5, abody frame 1 of a motorcycle includes a front block 3 that supports afront wheel suspension device 10 at the front end, and is provided witha pair of left and right main frames 2 that extend in the vehiclelongitudinal direction. Also, the reference sign 2L in FIG. 5 denotes aleft main frame, and the reference sign 2R denotes a right main frame.Further, the reference sign 3L in FIG. 5 denotes a left front block, andthe reference sign 3R denotes a right front block.

With reference to FIG. 1, the left and right main frames 2 include, inan integrated manner, front blocks 3 having such a shape that thefront-and-rear width is larger as it goes forward in side view, a pivotsection 5 that supports a rear wheel suspension device not illustrated,and a joining section 4 that extends so as to incline moderately so asto be positioned downward as it goes rearward from the rear end of thefront block 3 and extends between the rear end of the front block 3 andthe front upper end of the pivot section 5.

In a space below the main frames 2, an engine (not illustrated) forexample is mounted. Above the front block 3 and the joining section 4, afuel tank 7 is disposed. Above the pivot section 5, a seat 8 isdisposed. The vehicle body front part of the motorcycle is covered witha front cowl made of a synthetic resin.

Although it is not illustrated, the front block 3 has such a gate shape(inverted V-shape) of reducing the left-and-right width as it goesupward as viewed from the front and opening downward. In FIG. 1, thelower open section of the gate shape in the front block 3 is denoted bythe reference sign 3 s.

In addition, with reference to FIG. 2, in the front upper end of thefront block 3, an upper connection section 3 a is formed to which a rearend 21 b of an upper arm 21 is connected. In the front upper part of thefront block 3 and rearward of the upper connection section 3 a, ahandlebar support section 31 that supports a handlebar 18 is formed soas to extend rearward and upward. In the front lower part of the frontblock 3, a lower connection section 3 b is formed to which a rear end 22b of a lower arm 22 is connected.

With reference to FIG. 1, FIG. 2, and FIG. 5, a front wheel suspensiondevice 10 includes a front fork 17 that includes a steering shaft 16 atthe upper end and supports a front wheel 11 at the lower end. A steeringarm 45 is attached to the steering shaft 16, a handlebar post 35includes a steering force transmit member 38 turnably supported by asteering stem 39 arranged in the body frame 1, and a fork holder 15turnably (steerably) supports the front fork 17. A steering system link41 joins the steering arm 45 and the steering force transmit member 38,and a swing arm 20 includes upper and lower arms 21, 22 that extend inthe vehicle longitudinal direction and support the front wheel 11 in avertically swingable manner. A cushion member 27 that extends andshrinks accompanying the movement of the front wheel 11 and obtains adamping action. Through these handlebar post 35, steering system link41, steering arm 45, fork holder 15, and front fork 17, turning around asteering stem axis C1 accompanying the operation of the handlebar 18 andsteering of the front wheel 11 are interlocked. The handlebar post 35,the steering system link 41, the steering arm 45, the fork holder 15,and the front fork 17 form a steering system 60.

The steering force transmit member 38 is turned around the steering stemaxis C1 accompanying the operation of the handlebar 18. By turning thesteering force transmit member 38, a steering force is transmitted tothe steering shaft 16 through the steering system link 41. Bytransmission of the steering force to the steering shaft 16, the frontfork 17 is turned around a steering shaft axis C2.

Here, the steering stem axis C1 is the turning axis of the handlebarpost 35 that is rotated accompanying the operation of the handlebar 18,and agrees with the center axis of a boss section 32 of a cylindricalshape in the handlebar support section 31. The steering shaft axis C2 isthe turning axis of the front fork 17 that is turned accompanying theoperation of the handlebar 18, and agrees with the center axis of thefork holder 15 of a cylindrical shape. The angle of the steering shaftaxis C2 with respect to the vertical direction becomes “caster angle”.The steering shaft axis C2 offsets (departs) forward of the steeringstem axis C1 in side view. The steering shaft axis C2 and the steeringstem axis C1 are generally parallel to each other.

With reference to FIG. 1 and FIG. 2, the front fork 17 includes, in anintegrated manner, the steering shaft 16 that forms the steering shaftaxis C2, a pair of left and right arm sections 17 a that incline to bepositioned rearward as it goes upward in side view and extendvertically, and a cross member 17 b that joins the upper ends of theleft and right arms 17 a. The left and right arms 17 a are disposed onboth left and right sides of the front wheel 11. The cross member 17 bcurves inward in the vehicle width direction so as to line the treadsurface of the upper end position of the front wheel 11, and is disposedbetween the upper ends of the left and right arm sections 17 a. The leftand right ends of the cross member 17 b are joined to the upper ends ofthe left and right arms 17 a. Respective elements of the front fork 17are integrated aluminum components for example, and the respectiveelements are weld-joined so as to be integrated with each other.

The steering shaft 16 of the front fork 17 is supported by the forkholder 15 so as to be turnable around the steering shaft axis C2 at theinner side in the radial direction of the fork holder 15 of acylindrical shape. An upper end 16 a of the steering shaft 16 of thefront fork 17 is connected to the steering arm 45.

Although it is not illustrated, at the upper end of the cross member 17b, a journal section is formed to which a lower end 16 b of the steeringshaft 16 is connected. In the journal section of the cross member 17 b,an insertion hole (not illustrated) is formed which opens in a directionthe steering shaft 16 extends. By inserting the steering shaft 16through the insertion hole from the upper end 16 a and joining the lowerend 16 b of the steering shaft 16 and the journal section by welding ina state the lower end 16 b of the steering shaft 16 is positioned to theinsertion hole, the upper end of the cross member 17 b is fixed to thelower end 16 b of the steering shaft 16.

With reference to FIG. 1, to the lower end 17 d of the left and rightarms 17 a, an axle of the front wheel 11 (hereinafter referred to as“front wheel axle”) is connected. For example, both ends in the vehiclewidth direction of the front wheel axle are fixed to lower ends 17 d ofthe left and right arm sections 17 a through ball bearings notillustrated. A wheel of the front wheel 11 is turnably supported at thecenter in the vehicle width direction of the front wheel axle. By thecross member 17 b, a front fender 12 is supported through bolts notillustrated.

Also, the reference sign 13 in FIG. 1 denotes a brake caliper. Further,the reference sign 13 a denotes a brake rotor. Furthermore, thereference sign C10 denotes the center axis of the front wheel axle. Inaddition, the reference sign C10L denotes the perpendicular lowered froma center axis C10 to a road surface R. Also, the reference sign Tdenotes a trail.

With reference to FIG. 2, the handlebar support section 31 is arrangedso as to incline rearward with respect to the vertical line at the frontupper end of the front block 3 in side view. The handlebar supportsection 31 is arranged so as to be integrated with the upper end of thefront block 3 made of aluminum for example. The handlebar supportsection 31 turnably (steerably) supports the handlebar post 35.

With reference to FIG. 2 and FIG. 5 together, in other words, thehandlebar support section 31 is formed of the boss section 32 of acylindrical shape which forms the steering stem axis C1, and a left andright extension section 33 that extends rearward and upward from thefront upper end of the front block 3 so that the upper side ispositioned inward in the vehicle width direction and is connected to thelower end of the boss section 32. Also, the reference sign 33L in FIG. 5denotes the left extension section, and the reference sign 33R denotesthe right extension section.

In the left and right extension sections 33L, 33R, a bolt 34 a as ajoining shaft that extends along the vehicle width direction and joinsthe left and right extension sections 33L, 33R is arranged. In the leftand right extension sections 33L, 33R, a cushion upper connectionsection 27 c is formed to which an upper end 27 a of the cushion member27 is connected. At the upper end of the boss section 32, the handlebarpost 35 is arranged so as to be turnable around the steering stem axisC1.

With reference to FIG. 3 and FIG. 5, the handlebar post 35 is formed ofa holder 36 to which the handlebar 18 is fixed, and the steering stem 39that is connected to the lower part of the holder 36 and makes thesteering stem axis C1 the center axis. The holder 36 includes thesteering force transmit member 38 that has a thickness in a directionparallel to the steering stem axis C1, has a notch section in the sidepart in the left, and has a fan shape having a larger right-left widthas it goes forward as viewed from a direction along the steering stem39, and left and right extension sections 37L, 37R that are connected tothe front left and right both ends of the steering force transmit member38 and extend rearward and upward so as to form an L-shape in side view.

The steering stem 39 is turnably supported by the inner side in theradial direction of the boss section 32 through ball bearings (notillustrated). The steering force transmit member 38 is supported by theupper end of the steering stem 39 so as to be turnable around thesteering stem axis C1 through a collar and ball bearings (both are notillustrated). In addition, with reference to FIG. 6, at the right end ofthe steering force transmit member 38, a steering system link rearconnection section 38 c is formed to which the rear end of the steeringsystem link 41 is connected. To the steering force transmit member 38, asteering force transmit member side extension section 38 e is formedthat extends rearward making the left-right center line the vehicleleft-right center line CL as viewed from a direction along the steeringstem 39.

With reference to FIG. 3, FIG. 5, and FIG. 6, the left and rightextension sections 37L, 37R include, in an integrated manner, ahandlebar connection section 37 a to which the inner end in the vehiclewidth direction of the handlebar 18 is connected, a first extensionsection 37 b that is connected to a handlebar attaching section 38 aarranged at the left and right ends of the steering force transmitmember 38 and extends forward and upward in side view so as to line theslope of the steering force transmit member 38, and a second extensionsection 37 c that extends rearward and upward from the front upper endof the first extension section 37 b and is connected to the handlebarconnection section 37 a. The handlebar attaching section 38 a isdisposed forward of the steering stem 39 in side view. With reference toFIG. 6, the first extension section 37 b of the left and right extensionsections 37L, 37R is fastened and fixed to the handlebar attachingsection 38 a by plural (for example 2 pieces each for the left and theright in the present embodiment) fastening members (bolts).

Because the steering force transmit member 38 is turnably supported bythe steering stem 39, the handlebar post 35 is made turnable (steerable)around the steering stem axis C1 accompanying the operation of thehandlebar 18.

The reference sign 19L in the drawing denotes a left switch box thatincludes a switch group of a dimmer switch, a blinker switch, and thelike. Also, the reference sign 19R in FIG. 5 denotes a right switch boxthat includes a switch group of a kill switch, and the like. Further,the reference sign 19M in FIG. 5 denotes a master cylinder that isjoined to a brake lever.

With reference to FIG. 2, the fork holder 15 is arranged forward of thesteering stem axis C1 so as to be apart from the front block 3. In otherwords, the fork holder 15 has a cylindrical shape, and is arrangedforward of the front block 3 so as to incline rearward with respect tothe vertical direction. The fork holder 15 supports the steering shaft16 of the front fork 17 in the inner side in the radial directionthereof so as to be turnable (steerable) around the steering shaft axisC2. The upper end 16 a of the steering shaft 16 protrudes upward of anupper end 15 a of the fork holder 15. Also, the steering shaft 16 andthe fork holder 15 make the steering shaft axis C2 the center axis.

In a state the upper end 16 a of the steering shaft 16 protrudes upwardof an upper end 15 a of the fork holder 15, a ball bearing (notillustrated) that turnably supports the steering shaft 16 isincorporated between the steering shaft 16 and the fork holder 15 fromthe side of the upper end 16 a of the steering shaft 16. The referencesign 14 in the drawing denotes a slippage preventing member that isinserted into the steering shaft 16 from the side of the upper end 16 aof the steering shaft 16 and prevents slipping-off of the bearing.

With reference to FIG. 2 and FIG. 5, in the front upper part of the forkholder 15, an upper connection section 15 c to which a front end 21 a ofthe upper arm 21 is connected is formed so as to protrude forward andupward. In the rear lower part of the fork holder 15, a lower connectionsection 15 d to which a front end 22 a of the lower arm 22 is connectedis formed so as to protrude rearward and downward. The upper connectionsection 15 c is disposed forward of the steering shaft axis C2 in sideview, and the lower connection section 15 d is disposed rearward of thesteering shaft axis C2 in side view. On the left and right side surfacesof the fork holder 15, a rib 15 r for reinforcing the lower connectionsection 15 d is formed. The rib 15 r has a V-shape that opens forwardand upward in side view, and extends so as to diverge forward and upwardfrom the lower connection section 15 d so that the rib height increasesas it goes to the lower connection section 15 d side.

With reference to FIG. 3 and FIG. 5, the steering arm 45 is supported ina level higher than the upper end 15 a of the fork holder 15 by theupper end 16 a of the steering shaft 16. The steering arm 45 includes,in an integrated manner, a link front connection section 45 a to whichthe front end of an interlocking link 40 is connected, a journal section45 b having a C-shape in which the front as viewed from a directionalong the steering shaft axis C2 opens, and a joining section 45 c thatextends so as to be positioned outward in the vehicle width direction asit goes upward from the upper end of the journal section 45 b and joinsthe link front connection section 45 a and the journal section 45 b witheach other. The reference sign 45La in FIG. 5 denotes an assist steeringsystem link front connection section which is disposed on the left sidein the vehicle width direction and to which the front end of an assiststeering system link 73 forming the interlocking link 40 described belowis connected. Also, the reference sign 45Ra in FIG. 5 denotes a steeringsystem link front connection section which is disposed on the right sidein the vehicle width direction and to which the front end of thesteering system link 41 forming the interlocking link 40 is connected.

At the front end of the journal section 45 b, an insertion hole thatopens in the vehicle width direction is formed. For example, by screwingand fastening a bolt to a nut through the insertion hole in a state thejournal section 45 b is inserted to the upper end 16 a of the steeringshaft 16, the steering arm 45 is fastened and fixed to the upper end 16a of the steering shaft 16. The steering arm 45 is made turnable aroundthe steering shaft axis C2 integrally with the front fork 17accompanying the operation of the handlebar 18.

With reference to FIG. 5 and FIG. 6, the steering system link 41 isarranged on the right side in the vehicle width direction, and includesa steering system link member 42 having a linear shape extending forwardand rearward as viewed from the top. At the front end of the steeringsystem link member 42, a front ball joint 41F connected to the steeringsystem link front connection section 45Ra is arranged. At the rear endof the steering system link member 42, a rear ball joint 41R connectedto the steering system link rear connection section 38 c is arranged.

In FIG. 3, front and rear ball joints 73F, 73R in the assist steeringsystem link 73 having a configuration similar to that of the front andrear ball joints 41F, 41R in the steering system link 41 are shown.Similar to the front and rear ball joints 73F, 73R in the assiststeering system link 73, the front and rear ball joints 41F, 41R includeball studs 43 and sockets 44. The ball stud 43 includes a ball section43 a having a spherical shape, and a stud section 43 b that protrudesupward of the ball section 43 a. The ball section 43 a is slidably heldin the inside of the socket 44. The stud section 43 b extends linearlyin the vehicle top-bottom direction. The socket 44 includes upper andlower sockets 44 a, 44 b. Between the upper and lower sockets 44 a, 44b, the ball section 43 a is held slidably.

With reference to FIG. 2, FIG. 3, and FIG. 5, in the steering systemlink front connection section 45Ra, an insertion hole is formed whichopens in the vehicle top-bottom direction. By inserting a thread sectionof the upper end of the stud section 43 b of the front ball joint 41F tothe insertion hole of the steering system link front connection section45Ra and screwing and fastening a nut to the upward protruding portionthereof, the stud section 43 b of the front ball joint 41F is fastenedand fixed to the steering system link front connection section 45Ra.Below, the center axis of the stud section 43 b in the front ball jointwill be referred to as “the first axis C4”. The front end of thesteering system link member 42 is connected to the steering system linkfront connection section 45Ra through the front ball joint 41F so as tobe turnable around the first axis C4 (in other words, the center axis ofthe stud section 43 b in the front ball joint 41F on the right side inthe vehicle width direction).

In the steering system link rear connection section 38 c, an insertionhole is formed which opens in the vehicle top-bottom direction. Byinserting a thread section of the upper end of the stud section 43 b ofthe rear ball joint 41R to the insertion hole of the steering systemlink rear connection section 38 c and screwing and fastening a nut tothe upward protruding portion thereof, the stud section 43 b of the rearball joint 41R is fastened and fixed to the steering system link rearconnection section 38 c. Below, the center axis of the stud section 43 bin the rear ball joint will be referred to as “the second axis C5”. Therear end of the steering system link member 42 is connected to thesteering system link rear connection section 38 c through the rear balljoint 41R so as to be turnable around the second axis C5 (in otherwords, the center axis of the stud section 43 b in the rear ball joint41R on the right side in the vehicle width direction).

In the present embodiment, the steering system link member 42 includesthread sections at the front and rear ends, and is fixed using lock nutsin a state the front and rear thread sections are screwed by apredetermined amount to the rear end of the lower socket 44 b of thefront ball joint 41F and the front end of the lower socket 44 b of therear ball joint 41R respectively. Thus, by loosening the lock nuts andincreasing and reducing the screwing amount of the lower socket 44 b andthe thread sections, the distance between the front and rear connectionsections of the steering system link member 42 can be adjusted.

With reference to FIG. 2, the swing arm 20 includes the upper and lowerarms 21, 22 that extend in the vehicle longitudinal direction and arearranged so as to be vertically swingable. The upper and lower arms 21,22 are disposed side by side in the vehicle top-bottom direction, andextend along the vehicle longitudinal direction. The front end 21 a ofthe upper arm 21 is disposed on the outer side in the vehicle widthdirection of the upper part of the fork holder 15, and the front end 22a of the lower arm 22 is disposed on the inner side in the vehicle widthdirection of the lower part of the fork holder 15. The rear ends 21 b,22 b of the upper and lower arms 21, 22 are disposed on the inner sidein the vehicle width direction of the front part of the front block 3.The rear ends 21 b, 22 b of the upper and lower arms 21, 22 are storedwithin the lower open section 3 s of said gate shape in the front block3.

The front and rear ends 21 a, 21 b of the upper arm 21 are disposedforward of the front and rear ends 22 a, 22 b of the lower arm 22 inside view. In side view, the front end 21 a of the upper arm 21 ispositioned forward of the steering shaft axis C2, and the front end 22 aof the lower arm 22 is positioned rearward of the steering shaft axisC2. The rear ends 21 b, 22 b of the upper and lower arms 21, 22 areswingably supported by the front part of the front block 3. The forkholder 15 is swingably connected to the front ends 21 a, 22 a of theupper and lower arms 21, 22.

With reference to FIG. 2 and FIG. 5, the upper and lower connectionsections 15 c, 15 d of the fork holder 15 are swingably connected to thefront ends 21 a, 22 a of the upper and lower arms 21, 22 through bolts23 a, 25 a as joining shafts along the vehicle width direction. The bolt23 a penetrates the upper connection section 15 c of the fork holder 15and the front end 21 a of the upper arm 21, and extends in the vehiclewidth direction. The bolt 25 a penetrates the lower connection section15 d of the fork holder 15 and the front end 22 a of the lower arm 22,and extends in the vehicle width direction. The reference sign C11 inFIG. 2 denotes the center axis of the bolt 23 a that joins the upperconnection section 15 c of the fork holder 15 and the front end 21 a ofthe upper arm 21. The reference sign C13 in FIG. 2 denotes the centeraxis of the bolt 25 a that joins the lower connection section 15 d ofthe fork holder 15 and the front end 22 a of the lower arm 22.

The rear ends 21 b, 22 b of the upper and lower arms 21, 22 areswingably connected to the upper and lower connection sections 3 a, 3 bof the front block 3 through bolts 24 a, 26 a as joining shafts alongthe vehicle width direction. The bolt 24 a penetrates the rear end 21 bof the upper arm 21 and the upper connection section 3 a of the frontblock 3, and extends in the vehicle width direction. The bolt 26 apenetrates the rear end 22 b of the lower arm 22 and the lowerconnection section 3 b of the front block 3, and extends in the vehiclewidth direction. Because the rear ends 21 b, 22 b of the upper and lowerarms 21, 22 are turnably supported through the bolts 24 a, 26 a thatpenetrate the front block 3 and extend along the vehicle widthdirection, the upper and lower arms 21, 22 can be supported with highrigidity. The reference sign C12 in FIG. 2 denotes the center axis ofthe bolt 24 a that joins the rear end 21 b of the upper arm 21 and theupper connection section 3 a of the front block 3. The reference signC14 in FIG. 2 denotes the center axis of the bolt 26 a that joins therear end 22 b of the lower arm 22 and the lower connection section 3 bof the front block 3.

Below, the center axis of the bolt 23 a is referred to as “the firstjoining axis C11”, the center axis of the bolt 24 a is referred to as“the second joining axis C12”, the center axis of the bolt 25 a isreferred to as “the third joining axis C13”, and the center axis of thebolt 26 a is referred to as “the fourth joining axis C14”.

With reference to FIG. 2, in side view, a straight line passing throughthe first joining axis C11 and the second joining axis C12 is made “thefirst straight line AX1”, and a straight line passing through the thirdjoining axis C13 and the fourth joining axis C14 is made “the secondstraight line AX2”. In side view, the first straight line AX1 of theupper arm 21 and the second straight line AX2 of the lower arm 22 aregenerally parallel to each other.

In side view, the front-rear length of the upper arm 21 is generally thesame as the front-rear length of the lower arm 22. In other words, inside view, the length of the line segment connecting the first joiningaxis C11 and the second joining axis C12 is generally the same as thelength of the line segment connecting the third joining axis C13 and thefourth joining axis C14. Thus, the fork holder 15 moves upward anddownward generally in parallel with each other with respect to verticalswinging of the upper and lower arms 21, 22. The rear end 21 b of theupper arm 21 (the second joining axis C12) and the front end 22 a of thelower arm 22 (the third joining axis C13) are disposed between thesteering shaft axis C2 and a stroke axis C3 described below in sideview.

With reference to FIG. 2 and FIG. 5, the upper arm 21 includes, in anintegrated manner, a pair of left and right upper arm bodies 21 c thatextend forward and rearward, and a cross member 21 d that joins the rearends 21 b of the left and right upper arm bodies 21 c. The respectiveelements of the upper arm 21 are components made of aluminum forexample, and are formed so as to be integrated with each other.

The left and right upper arm bodies 21 c are disposed on both left andright sides of the upper part of the fork holder 15. The left and rightupper arm bodies 21 c curve inward in the vehicle width direction so asto line the outer wall surface of the upper part of the fork holder 15.

At the front ends 21 a of the left and right upper arm bodies 21 c,insertion holes that open in the vehicle width direction are formed. Ina state the upper connection section 15 c of the fork holder 15 issandwiched between the front ends 21 a of the left and right upper armbodies 21 c, the bolt 23 a is screwed and fastened to a nut 23 b throughthe insertion holes (the insertion holes of the front ends 21 a of theleft and right upper arm bodies 21 c) and the inner periphery of theupper connection section 15 c. The upper connection section 15 c of thefork holder 15 is supported by the front end 21 a of the upper arm 21through a collar and ball bearings (both are not illustrated) so as tobe turnable around the first joining axis C11.

In the upper connection sections 3 a of the left and right front blocks3L, 3R, insertion holes that open in the vehicle width direction areformed. In a state the rear end 21 b of the upper arm 21 (the rear end21 b of the left and right upper arm bodies 21 c and the cross member 21d) is sandwiched between the upper connection sections 3 a of the leftand right front blocks 3L, 3R, the bolt 24 a is screwed and fastened toa nut 24 b through the insertion holes (the insertion holes of the upperconnection sections 3 a of the left and right front blocks 3L, 3R) andthe inner periphery of the rear end 21 b of the upper arm 21. The rearend 21 b of the upper arm 21 is supported by the upper connectionsections 3 a of the left and right front blocks 3L, 3R through a collarand ball bearings (both are not illustrated) so as to be turnable aroundthe second joining axis C12.

With reference to FIG. 2 and FIG. 5, the lower arm 22 includes, in anintegrated manner, a pair of left and right lower arm bodies 22 c thatextend forward and rearward, a front cross member (not illustrated) thatjoins the front ends 22 a of the left and right lower arm bodies 22 c,and a rear cross member 22 d that joins the rear ends 22 b of the leftand right lower arm bodies 22 c. The respective elements of the lowerarm 22 are components made of aluminum for example, and are formed so asto be integrated with each other. The left and right lower arm bodies 22c are disposed on both left and right sides of the lower part of thecushion member 27.

In the left and right lower connection sections 15 d protruding rearwardfrom the rear left and right parts of the fork holder 15, insertionholes that open in the vehicle width direction are formed. In a statethe front end 22 a of the left and right lower arm bodies 22 c (thefront end 22 a of the left and right lower arm bodies 22 c and the frontcross member) is sandwiched between the left and right lower connectionsections 15 d, the bolt 25 a is screwed and fastened to a nut (notillustrated) through the insertion holes (the insertion holes of theleft and right connection sections 15 d) and the inner periphery of thefront end 22 a of the left and right lower arm bodies 22 c. The left andright lower connection sections 15 d of the fork holder 15 are supportedby the front end 22 a of the lower arm 22 through a collar and ballbearings (both are not illustrated) so as to be turnable around thethird joining axis C13.

In the lower connection section 3 b of the front block 3, an insertionhole that opens in the vehicle width direction is formed. In a state therear end 22 b of the lower arm 22 (the rear end 22 b of the left andright lower arm bodies 22 c and the rear cross member 22 d) issandwiched between the lower connection sections 3 b of the front block3, the bolt 26 a is screwed and fastened to a nut 26 b through theinsertion holes (the insertion holes of the lower connection sections 3b of the front block 3) and the inner periphery of the rear ends 22 b ofthe lower arm 22. The rear end 22 b of the lower arm 22 is supported bythe lower connection sections 3 b of the front block 3 through a collarand ball bearings (both are not illustrated) so as to be turnable aroundthe fourth joining axis C14.

In the lower arm 22, behind the center part in the vehicle widthdirection of the front cross member and at the front ends 22 a of theleft and right lower arm bodies 22 c, a cushion lower connection section27 d is formed to which a lower end 27 b of the cushion member 27 isconnected.

With reference to FIG. 2, the cushion member 27 includes a damper 27 jof a rod type which inclines so as to be positioned rearward as it goesupward in side view, and a coil spring 27 k that is wound around theperiphery of the damper 27 j. The cushion member 27 extends and shrinksby stroking along its center axis C3, and secures a predetermineddamping action. Below, the center axis C3 is referred to as “strokeaxis”. The cushion upper connection section 27 c is disposed rearward ofthe steering stem axis C1 so that the stroke axis C3 inclines rearwardwith respect to the vertical direction in side view.

The cushion member 27 makes the lower end 27 b stroke accompanyingswinging of the lower arm 22, and secures the damping action. Thecushion member 27 is disposed forward and upward of an engine andrearward and upward of the front wheel 11 in side view. The upper partof the cushion member 27 is stored within the lower open section 3 s ofsaid gate shape in the front block 3. The upper end 27 a of the cushionmember 27 is covered by the front block 3 in side view.

With reference to FIG. 2 and FIG. 5, the upper end 27 a of the cushionmember 27 is swingably connected to the cushion upper connection section27 c of the left and right extension sections 33L, 33R, and the lowerend 27 b of the cushion member 27 is swingably connected to the cushionlower connection section 27 d of the lower arm 22.

The upper end 27 a of the cushion member 27 is swingably connected tothe cushion upper connection section 27 c of the left and rightextension sections 33L, 33R through the bolt 34 a as a joining shaftalong the vehicle width direction. The bolt 34 a penetrates the cushionupper connection section 27 c and the upper end 27 a of the cushionmember 27, and extends in the vehicle width direction. The referencesign C15 in FIG. 2 denotes the center axis of the bolt 34 a that joinsthe cushion upper connection section 27 c and the upper end 27 a of thecushion member 27.

In the cushion upper connection sections 27 c of the left and rightextension sections 33L, 33R, insertion holes that open in the vehiclewidth direction are formed. In a state where the upper end 27 a of thecushion member 27 is sandwiched between the cushion upper connectionsections 27 c of the left and right extension sections 33L, 33R, thebolt 34 a is inserted through the insertion holes (the insertion holesof the cushion upper connection sections 27 c of the left and rightextension sections 33L, 33R) and the inner periphery of the upper end 27a of the cushion member 27, and a nut (not illustrated) is screwed andfastened to the protruding portion thereof. The upper end 27 a of thecushion member 27 is supported by the cushion upper connection sections27 c of the left and right extension sections 33L, 33R through a collar(not illustrated) so as to be turnable around the center axis C15.

The lower end 27 b of the cushion member 27 is swingably connected tothe left and right cushion lower connection sections 27 d of the lowerarm 22 through a bolt 28 a as a joining shaft along the vehicle widthdirection. The bolt 28 a penetrates the cushion lower connectionsections 27 d and the lower end 27 b of the cushion member 27, andextends in the vehicle width direction. The reference sign C16 in FIG. 2denotes the center axis of the bolt 28 a that joins the cushion lowerconnection sections 27 d and the lower end 27 b of the cushion member27.

In the left and right cushion lower connection sections 27 d of thelower arm 22, insertion holes that open in the vehicle width directionare formed. In a state where the lower end 27 b of the cushion member 27is sandwiched between the left and right cushion lower connectionsections 27 d of the lower arms 22, the bolt 28 a is inserted throughthe insertion holes (the insertion holes of the left and right cushionlower connection sections 27 d of the lower arm 22) and the innerperiphery of the lower end 27 b of the cushion member 27, and a nut (notillustrated) is screwed and fastened to the protruding portion thereof.The lower end 27 b of the cushion member is supported by the left andright cushion lower connection sections 27 d of the lower arm 22 througha collar (not illustrated) so as to be turnable around the center axisC16.

Below, actions of the cushion member 27 will be described.

When the front wheel 11 deflects relatively upward by front wheelbraking and the like from the 1G state in which a load of the vehicleweight portion is applied to the front wheel suspension device 10, theswing arm 20 swings upward, and the front fork 17 and the fork holder 15deflect upward. At this time, the lower arm 22 turns rearward in theright turn (clockwise) in FIG. 2 around the fourth joining axis C14.Then, the lower arm 22 makes the lower end 27 b of the cushion member 27deflect upward, and compresses the cushion member 27.

When the fork holder 15 deflects upward, the steering arm 15 alsodeflects integrally responding it. At this time, although the steeringsystem link member 42 (referring to FIG. 5) deflects with respect to thehandlebar post 35 and the angle of the steering shaft axis C2 withrespect to the steering stem axis C1 changes, this change is absorbed byswinging of the front and rear ball joints 41F, 41R and swinging of thesteering system link member 42.

On the other hand, when the front wheel 11 deflects relatively downwardby acceleration and the like from said 1G state, the swing arm 20 swingsdownward, and the front fork 17 and the fork holder 15 deflect downward.At this time, the lower arm 22 turns forward in the left turn(counter-clockwise) in FIG. 2 around the fourth joining axis C14. Then,the lower arm 22 makes the lower end 27 b of the cushion member 27deflect downward, and extends the cushion member 27.

When the fork holder 15 deflects downward, the steering arm 45 alsodeflects integrally responding it. At this time, although the steeringsystem link member 42 deflects with respect to the handlebar post 35 andthe angle of the steering shaft axis C2 with respect to the steeringstem axis C1 changes, this change is absorbed by swinging of the frontand rear ball joints 41F, 41R and swinging of the steering system linkmember 42.

With reference to FIG. 1, the steering system 60 further includes apower assist unit 70 that assists the steering force transmitted to thesteering shaft 16. With reference to FIG. 2 and FIG. 5 together, thepower assist unit 70 includes an assist motor 71 that generates asteering assist force assisting the steering force transmitted to thesteering shaft 16, a steering assist force transmit member 72 that isturnably supported by the steering stem 39, an assist steering systemlink 73 that joins the steering arm 45 and the steering assist forcetransmit member 72, a steering assist force transmit mechanism 75 thattransmits the steering assist force generated by the assist motor 71 (inother words, outputted by an output shaft 71 b described below) to thesteering assist force transmit member 72, a steering assist forcetransmit arm 78, and a steering assist force transmit rod 79. Thesteering system link 41 and the assist steering system link 73 form theinterlocking link 40.

With reference to FIG. 2, the assist motor 71 is disposed adjacent tothe assist steering system link 73 at the left side of the assiststeering system link 73. The assist motor 71 is disposed between thesteering shaft 16 and the steering stem 39 in side view. In other words,the assist motor 71 is disposed closer to the steering shaft axis C2 inthe region between the steering stem axis C1 and the steering shaft axisC2 in side view.

The assist motor 71 includes a motor body 71 a, and the output shaft 71b that outputs the rotative drive of the motor body 71 a as the steeringassist force. In the front upper part of the motor body 71 a, a motorharness 71 c is attached which is connected to an ECU 90 (referring toFIG. 5) described below. The motor body 71 a and the output shaft 71 bextend in a direction along the steering shaft axis C2 in side view. Themotor body 71 a is disposed downward of the front end of the steeringassist force transmit mechanism 75. The output shaft 71 b is orientedupward so as to protrude upward from the upper end of the motor body 71a. The lower part of the motor body 71 a overlaps with the front-rearmiddle part of the upper arm body 21 c in side view.

Below, the rotation axis of the assist motor 71 is made a motor axis Cm.The motor axis Cm agrees with the center axis of the motor body 71 athat has a cylindrical shape. The motor axis Cm offsets (departs)rearward of the steering shaft axis C2 in side view. The motor axis Cmand the steering shaft axis C2 are generally parallel to each other.

With reference to FIG. 2 and FIG. 6, the steering assist force transmitmember 72 is turned around the steering stem axis C1 accompanying therotative drive of the assist motor 71. By turning of the steering assistforce transmit member 72, the steering assist force is transmitted tothe steering shaft 16 through the assist steering system link 73. Bytransmission of the steering assist force to the steering shaft 16,turning of the front fork 17 around the steering shaft axis C2 isassisted.

The steering assist force transmit member 72 has a thickness in adirection parallel to the steering stem axis C1, and has a shape ofextending leftward and rearward in the radial direction (the directionorthogonal to the steering stem axis C1) as viewed from a directionalong the steering stem 39. The steering assist force transmit member 72is disposed downward of the steering force transmit member 38. Thesteering assist force transmit member 72 is supported by the steeringstem 39 through a collar and ball bearings (both are not illustrated) soas to be turnable around the steering stem axis C1. At the front end(left end) of the left hand extension section of the steering assistforce transmit member 72, an assist steering system link rear connectionsection 72 c is formed to which the rear end of the assist steeringsystem link 73 is connected. In the steering assist force transmitmember 72, a steering assist force transmit member side extensionsection 72 e is formed which extends rearward making the left-rightcenter line the vehicle left-right center line CL as viewed from adirection along the steering stem 39. In the steering assist forcetransmit member side extension section 72 e, a steering assist forcetransmit rod second connection section 72 j is arranged to which thesecond end (one end) 79 b of the steering assist force transmit rod 79described below is connected.

The steering force transmit member 38 and the steering assist forcetransmit member 72 are disposed so that a part thereof overlapsvertically. In other words, the steering force transmit member 38 andthe steering assist force transmit member 72 are disposed so that thesteering force transmit member side extension section 38 e and thesteering assist force transmit member side extension section 72 eoverlap vertically. The left hand extension section of the steeringassist force transmit member 72 (the assist steering system link rearconnection section 72 c) is exposed upward from the left side notchsection of the steering force transmit member 38 as viewed from adirection along the steering stem 39.

With reference to FIG. 2, FIG. 5, and FIG. 6, the assist steering systemlink 73 includes an assist steering system link member 74 having alinear shape that extends forward and rearward in side view and topview. At the front end of the assist steering system link member 74, thefront ball joint 73F is arranged which is connected to the assiststeering system link front connection section 45La. At the rear end ofthe assist steering system link member 74, the rear ball joint 73R isarranged which is connected to the assist steering system link rearconnection section 72 c.

With reference to FIG. 2, the front and rear ball joints 73F, 73Rinclude the ball studs 43 and the sockets 44. Because the ball stud 43and the socket 44 in the front and rear ball joints 73F, 73R have aconfiguration same as that in the front and rear ball joints 41F, 41Rdescribed above, the detailed description thereof will be omitted.

With reference to FIG. 2, FIG. 5, and FIG. 6, in the assist steeringsystem link front connection section 45La, an insertion hole that opensin the vehicle top-bottom direction is formed. By inserting the threadsection of the upper end of the stud section 43 b of the front balljoint 73F to the insertion hole of the assist steering system link frontconnection section 45La and screwing and fastening a nut to the upwardprotruding portion thereof, the stud section 43 b of the front balljoint 73F is fastened and fixed to the assist steering system link frontconnection section 45La. The front end of the assist steering systemlink member 74 is connected to the assist steering system link frontconnection section 45La through the front ball joint 73F so as to beturnable around the first axis C4 (in other words, the center axis ofthe stud section 43 b in the front ball joint 73F on the left side inthe vehicle width direction).

In the assist steering system link rear connection section 72 c, aninsertion hole that opens in the vehicle top-bottom direction is formed.By inserting the thread section of the upper end of the stud section 43b of the rear ball joint 73R to the insertion hole of the assiststeering system link rear connection section 72 c and screwing andfastening a nut to the upward protruding portion thereof, the studsection 43 b of the rear ball joint 73R is fastened and fixed to theassist steering system link rear connection section 72 c. The rear endof the assist steering system link member 74 is connected to the assiststeering system link rear connection section 72 c through the rear balljoint 73R so as to be turnable around the second axis C5 (in otherwords, the center axis of the stud section 43 b in the rear ball joint73R on the left side in the vehicle width direction).

In the present embodiments, the assist steering system link member 74includes thread sections at the front and rear ends, and is fixed usinglock nuts in a state the front and rear thread sections are screwed by apredetermined amount to the rear end of the lower socket 44 b of thefront ball joint 73F and the front end of the lower socket 44 b of therear ball joint 73R respectively. Thus, by loosening the lock nut andincreasing and reducing the screwing amount of the lower socket 44 b andthe thread section, the distance between the front and rear connectionsections of the assist steering system link member 74 can be adjusted.

With reference to FIG. 3 and FIG. 5, the steering assist force transmitmechanism 75 includes a gear box 76 that stores speed reduction gears(not illustrated) in the inside, and a gear box cover 77 that covers theupper part of the gear box 76. The front upper part of the steeringassist force transmit mechanism 75 overlaps with the front part of theassist steering system link 73 in side view.

The assist motor 71 and the steering assist force transmit mechanism 75are disposed side by side in the vehicle longitudinal direction. Asviewed from a direction along the steering stem 39, the assist motor 71and the steering assist force transmit mechanism 75 are disposedadjacent to the assist steering system link 73 at the left side of theassist steering system link 73.

The gear box 76 has a thickness in a direction parallel to the motoraxis Cm, and is arranged so as to incline rearward with respect to thevertical direction at the left side of the assist steering system link73 in side view. In the gear box 76, a drive gear that is fixedcoaxially with the output shaft 71 b of the assist motor 71, an idlegear that engages with the drive gear, and a driven gear (all of themare not illustrated) that is rotatively driven through the idle gear arestored. The driven gear is coaxially fixed to a transmission shaft 76 athat extends in parallel with the output shaft 71 b. The transmissionshaft 76 a is disposed rearward of the output shaft 71 b and leftward ofthe steering stem 39.

The gear box 76 includes, in an integrated manner, a front side storingsection that is positioned on the front right side as viewed from adirection along the steering stem 39, stores the drive gear, and has acircular shape, a rear side storing section that is positioned in therear part, stores the driven gear and the transmission shaft 76 a, andhas such a shape of combining a fan shape and a circular shape, and amiddle storing section that is positioned in the front-rear middle part,stores the idle gear, and connects the front side storing section andthe rear side storing section. In the upper outer peripheral part of thegear box 76 as viewed in a direction along the steering stem 39, gearbox cover attaching sections of plural numbers (7 pieces for example inthe present embodiment) for attaching the gear box cover 77 are formedso as to protrude outward with intervals along said upper outerperipheral part.

The gear box cover 77 has a thickness thinner than that of the gear box76 along a direction parallel to the motor axis Cm. The gear box cover77 is fastened and fixed to the gear box cover attaching sections in thegear box 76 by bolts 77 a of plural numbers (7 pieces for example in thepresent embodiment) fastening from the vehicle upper side.

With reference to FIG. 2, FIG. 3, and FIG. 6, to the upper end of thetransmission shaft 76 a, the front end of the steering assist forcetransmit arm 78 is fixed which inclines rearward with respect to thevertical direction at the left side of the assist steering system link73 in side view and extends forward and rearward as viewed from adirection along the steering stem 39. The steering assist force transmitarm 78 is made swingable around the transmission shaft 76 a.

The steering assist force transmit arm 78 is formed so that the widththereof gently reduces as it departs from the transmission shaft 76 a(so that the left-right width gently reduces as it goes rearward in FIG.6) as viewed from a direction along the transmission shaft 76 a. At therear end of the steering assist force transmit arm 78, a steering assistforce transmit rod first connection section 78 j is arranged to which afirst end 79 a (the left end in the vehicle width direction) of thesteering assist force transmit rod 79 is connected. Below, the centeraxis of the transmission shaft 76 a is made a transmission axis C20. Thetransmission axis C20 and the motor axis Cm are generally parallel toeach other.

With reference to FIG. 2 and FIG. 6, the steering assist force transmitrod 79 has a linear shape that extends in the vehicle width direction asviewed from a direction along the steering stem 39. The first end 79 a(the left end in the vehicle width direction) of the steering assistforce transmit rod 79 is connected to the steering assist force transmitrod first connection section 78 j by the ball joint. The steering assistforce transmit rod 79 is connected to the steering assist force transmitrod first connection section 78 j through the ball joint so as to beturnable around a center axis C21 of a stud section (not illustrated) inthe ball joint.

A second end 79 b (the right end in the vehicle width direction) of thesteering assist force transmit rod 79 is connected to the steeringassist force transmit rod connection section 72 j by the ball joint. Thesteering assist force transmit rod 79 is connected to the steeringassist force transmit rod connection section 72 j through the ball jointso as to be turnable around a center axis C22 of a stud section (notillustrated) in the ball joint. The respective center axes C21, C22 andthe transmit axis C20 are generally parallel to each other.

With reference to FIG. 6, in the steering system link 41, a steeringforce detection sensor 42 a is arranged which detects a steering forcetransmitted to the steering shaft 16. The steering force detectionsensor 42 a detects a tension force and a compression force applied inthe axial direction of the steering system link member 42. The steeringforce detection sensor 42 a is built in the steering system link member42. For example, the steering force detection sensor 42 a uses a straingage type load cell. Also, the steering force detection sensor 42 a isnot limited to it, and a magnetostrictive type load cell and anelectrostatic capacitance type load cell may be used.

With reference to FIG. 6, the detection value of the steering forcedetection sensor 42 a is inputted to the ECU 90 (Electronic ControlUnit) as a control unit that controls the motion of the assist motor 71.The ECU 90 is attached to the steering stem 39 through a first bracket91 and a second bracket 92.

The first bracket 91 is disposed downward of the steering assist forcetransmit member 72. The first bracket 91 includes a fixed section 39 athat is fixed to the steering stem 39, and left and right front sidebranching pieces 91 b, 91 c that branch left and right forward from thefront part of the fixed section 39 a and support the second bracket 92.The second bracket 92 includes a body section 92 a that supports the ECU90, and left and right rear side branching pieces 92 b, 92 c that branchleft and right rearward from the rear part of the body section 92 a andare supported by the left and right front side branching pieces 91 b, 91c of the first bracket 91 respectively.

The ECU 90 controls the assist motor 71 based on the detection result ofthe steering force detection sensor 42 a. The ECU detects a steeringforce (steering torque) of the handlebar applied to the steering shaft16 from a detection value of the steering force detection sensor 42 a,and drivingly controls the assist motor 71 so that the steering forcedoes not become excessive.

For example, the ECU 90 drivingly controls the assist motor 71 so thatthe steering assist force that assists the steering force increases whenthe motorcycle is in a stopping state or in a low vehicle speed state,and drivingly controls the assist motor 71 so that the steering assistforce reduces when the motorcycle is in a middle/high vehicle speedstate. In other words, the ECU 90 drivingly controls the assist motor 71so that the steering assist force increases as the vehicle speed of themotorcycle reduces, and drivingly controls the assist motor 71 so thatthe steering assist force reduces as the vehicle speed of the motorcycleincreases. Thus, steering of the handlebar can be made light as thevehicle speed of the motorcycle reduces, and steering of the handlebarcan be made heavy as the vehicle speed of the motorcycle increases.

Also, from the viewpoint of improving the handlebar operability when themotorcycle is in a stopping state or in a low vehicle speed state (fromthe viewpoint of facilitating handlebar operation at the time of parkingfor example), the ECU 90 may drivingly control the assist motor 71 usingan intermediary value between the maximum value and the minimum value ofthe steering assist force as the steering assist force when themotorcycle is in a stopping state or in a low vehicle speed state.

With reference to FIG. 3 and FIG. 9, between the steering force transmitmember 38 and the steering assist force transmit member 72, engagesections 38 d, 72 d (a steering force transmit member side engagesection 38 d and a steering assist force transmit member side engagesection 72 d) are arranged that allow the steering force transmit member38 and the steering assist force transmit member 72 to engage with eachother so that the steering assist force transmit member 72 are turnedaround the steering stem 39 accompanying turning of the steering forcetransmit member 38. The engage sections 38 d, 72 d are formed betweenthe steering force transmit member side extension section 38 e and thesteering assist force transmit member side extension section 72 e.

The steering force transmit member side engage section 38 d is a recessthat is recessed forward in a rectangular shape from the rear end of thesteering force transmit member side extension section 38 e as viewedfrom a direction along the steering stem 39. The steering assist forcetransmit member side engage section 72 d is a projection that protrudesrearward and upward from the rear end of the steering assist forcetransmit member side extension section 72 e in side view and has arectangular shape that extends forward and rearward as viewed from adirection along the steering stem 39.

The steering force transmit member 38 and the steering assist forcetransmit member 72 are disposed with a gap 38 s in the turning direction(the direction around the center axis C22) in the engage sections 38 d,72 d. The gap 38 s is a space between the inner peripheral surface ofthe steering force transmit member side engage section 38 d that is arecess recessed in a rectangular shape as viewed from a direction alongthe steering stem 39 and the outer peripheral surface of the steeringassist force transmit member side engage section 72 d that is aprojection having a rectangular shape that extends forward and rearward.The size of the gap 38 s is made a constant size in said turningdirection.

With reference to FIG. 4, to the body frame 1, a stay 80 is attachedwhich supports vehicle components. The stay 80 includes a first stay 81in which a lower end 81 a is fastened and fixed to the left side part ofthe front block 3 by bolts of plural numbers (2 pieces for example inthe present embodiment) arrayed vertically and which curves rearward andupward from the fastening part of the upper bolt in side view andthereafter curves and extends forward and upward, a second stay 82 inwhich a rear lower end 82 a is fastened and fixed to the front upper endof the first stay 81 by bolts of plural numbers (2 pieces for example inthe present embodiment) arrayed in front and rear and which gentlyinclines and extends forward and upward from the fastening part of thefront bolt in side view and thereafter curves forward and upward toextend forward and upward more sharply than in the rear side, a thirdstay 83 in which a lower end 83 a is fastened and fixed to the front endof the front block 3 by a bolt from the front, which extends upward fromthe fastening part of the bolt in side view, thereafter curves andextends forward and upward, thereafter curves and extends rearward andupward, and in which the upper end is weld-joined to the front upperpart of the second stay 82, a fourth stay 84 in which a head lightsupport section 84 a that supports a head light (not illustrated) isarranged at the front lower end, which inclines gently and extendsrearward and upward from a head light support section 84 a in side view,and in which the rear upper end is weld-joined to the front lower partof the third stay 83, and a sub-stay 85 which extends between the curvedpart of the second stay 82 and the front lower part of the third stay83, and inclines and extends so as to be positioned downward as it goesforward in side view with the front end being weld-joined to the frontlower part of the third stay 83 and with the rear end being weld-joinedto the curved part of the second stay 82.

At the front upper end of the second stay 82, a vehicle componentattaching section 86 is arranged which supports vehicle components suchas a front cowl 9, a visor, and a meter unit (all of them are notillustrated). At the rear lower part of the third stay 83, an assistmotor support section 87 is arranged which supports the assist motor 71.The assist motor support section 87 has a cylindrical shape that canstore the lower part of the motor body 71 a. In the assist motor supportsection 87, an opening section 87 h is formed which opens in the vehiclewidth direction and forms a circular shape in side view.

Also, from the viewpoint of effectively reducing the vibration of theassist motor 71, the assist motor support section 87 may be configuredto support the lower part of the motor body 71 a through an elasticmember such as rubber or a damping material obtained by foaming asynthetic resin and the like (both are not illustrated).

As described above, according to the above-described embodiments, in thesteering system 60 of a saddle-ride type vehicle including the frontfork 17 that includes the steering shaft 16 at the upper end andsupports the front wheel 11 at the lower end, the steering arm 45 thatis attached to the steering shaft 16, the steering force transmit member38 that is turnably supported by the steering stem 39 that is arrangedin the body frame 1, and the steering system link 41 that joins thesteering arm 45 and the steering force transmit member 38, the assistmotor 71 that generates a steering assist force that assists a steeringforce transmitted to the steering shaft 16, the steering assist forcetransmit member 72 that is turnably supported by the steering stem 39,and the assist steering system link 73 that joins the steering arm 45and the steering assist force transmit member 72 are further provided,and the assist motor 71 is disposed adjacent to the assist steeringsystem link 73.

According to this configuration, because the assist motor 71 is disposedadjacent to the assist steering system link 73, a space adjacent to theassist steering system link 73 can be effectively utilized in disposingthe assist motor 71, and therefore enlargement of the steering system 60can be suppressed.

Also, according to the above-described embodiments, because the assistmotor 71 is disposed between the steering shaft 16 and the steering stem39 in side view, the assist motor 71 comes to be positioned rearward ofthe front fork 17, and therefore the assist motor 71 can be protectedeasily.

Also, according to the above-described embodiments, because at least apart of the assist motor 71 overlaps with the swing arm 20 in side view,a space at the side of the swing arm 20 can be effectively utilized indisposing the assist motor 71, and therefore the assist motor 71 can bedisposed compactly.

Also, according to the above-described embodiments, because the motorbody 71 a is disposed downward of the steering assist force transmitmechanism 75 and the output shaft 71 b is directed upward, compared tothe case the motor body 71 a is disposed upward of the steering assistforce transmit mechanism 75 and the output shaft 71 b is directeddownward, the motor body 71 a that is relatively heavy in the assistmotor 71 can be disposed at a low position, and therefore the positionof the center of gravity of the vehicle can be lowered.

Also, according to the above-described embodiments, because at least apart of the steering assist force transmit mechanism 75 overlaps withthe assist steering system link 73 in side view, a space at the side ofthe assist steering system link 73 can be effectively utilized indisposing the steering assist force transmit mechanism 75, and thereforethe steering assist force transmit mechanism 75 can be disposedcompactly.

Also, according to the above-described embodiments, because the assistmotor support section 87 that supports the assist motor 71 is arrangedin the stay 80, compared to the case a support member for supporting theassist motor 71 is arranged separately and independently, the number ofpieces of components can be suppressed. Further, compared to the casethe assist motor 71 is not supported, the vibration of the assist motor71 can be reduced.

Also, the present invention is not limited to the above embodiments. Forexample, in the saddle-ride type vehicle, general vehicles in which arider sits astride a vehicle body are included, and, not onlymotorcycles (including motor-assisted bicycles and scooter-typevehicles) but also three-wheeled vehicles (in addition to one frontwheel and two rear wheel vehicles, two front wheel and one rear wheelvehicles are included) are included.

Further, the configuration in the above embodiments is an example of thepresent invention, and various alterations are possible within a scopenot deviating from the substance of the present invention such that theconstituent element of the embodiment is substituted by a knownconstituent element.

REFERENCE SIGNS LIST

-   1 . . . Body frame-   11 . . . Front wheel-   15 . . . Fork holder-   16 . . . Steering shaft-   17 . . . Front fork-   18 . . . Handlebar-   20 . . . Swing arm-   38 . . . Steering force transmit member-   38 a . . . Handlebar attaching section-   38 d . . . Engage section-   38 e . . . Steering force transmit member side extension section-   38 s . . . Gap-   39 . . . Steering stem-   41 . . . Steering system link-   42 . . . Steering system link member-   42 a . . . Steering force detection sensor-   45 . . . Steering arm-   45La . . . Assist steering system link front connection section-   45Ra . . . Steering system link front connection section-   60 . . . Steering system-   71 . . . Assist motor-   71 a . . . Motor body-   71 b . . . Output shaft-   72 . . . Steering assist force transmit member-   72 d . . . Engage section-   72 e . . . Steering assist force transmit member side extension    section-   72 j . . . Steering assist force transmit rod second connection    section-   73 . . . Assist steering system link-   75 . . . Steering assist force transmit mechanism-   79 . . . Steering assist force transmit rod-   79 b . . . Second end (one end) of steering assist force transmit    rod-   80 . . . Stay-   87 . . . Assist motor support section

The invention claimed is:
 1. A steering system of a saddle-ride typevehicle, said system comprising: a front fork that includes a steeringshaft at an upper end and supports a front wheel at a lower end; asteering arm attached to the steering shaft; a steering force transmitmember that is turnably supported by a steering stem that is disposed ina body frame; a steering system link that joins the steering arm and thesteering force transmit member; an assist motor configured to generate asteering assist force that assists a steering force transmitted to thesteering shaft; a steering assist force transmit member that is turnablysupported by the steering stem; and an assist steering system link thatjoins the steering arm and the steering assist force transmit member,wherein the assist motor is disposed adjacent to the assist steeringsystem link.
 2. The steering system of a saddle-ride type vehicleaccording to claim 1, wherein the assist motor is disposed between thesteering shaft and the steering stem in side view.
 3. The steeringsystem of a saddle-ride type vehicle according to claim 1, wherein thebody frame is connected to a rear end of a swing arm that extendsvehicle forward and rearward and is made vertically swingable, wherein afront end of the swing arm is connected to a fork holder that steerablysupports the front fork, and wherein at least a part of the assist motoroverlaps with the swing arm in side view.
 4. The steering system of asaddle-ride type vehicle according to claim 1, wherein the assist motorincludes a motor body, and an output shaft that is configured to outputrotational drive of the motor body as the steering assist force, whereina steering assist force transmit mechanism is configured to transmit thesteering assist force outputted by the output shaft to the steeringshaft is provided, wherein the motor body is disposed downward of thesteering assist force transmit mechanism, and wherein the output shaftis directed upward.
 5. The steering system of a saddle-ride type vehicleaccording to claim 4, wherein at least a part of the steering assistforce transmit mechanism overlaps with the assist steering system linkin side view.
 6. The steering system of a saddle-ride type vehicleaccording to claim 1, further comprising a stay configured to supportvehicle components, said stay being attached to the body frame, whereinthe stay is provided with an assist motor support section that supportsthe assist motor.
 7. A steering system of a saddle-ride type vehicle,said system comprising: front fork means including steering shaft meansat an upper end thereof, said front fork means for supporting a frontwheel at a lower end thereof; steering arm means attached to thesteering shaft means; steering force transmit means for being turnablysupported by steering stem means disposed in a body frame; steeringsystem link means for joining the steering arm means and the steeringforce transmit means; assist motor means for generating a steeringassist force that assists a steering force transmitted to the steeringshaft means; steering assist force transmit means for being turnablysupported by the steering stem means; and assist steering system linkmeans for joining the steering arm means and the steering assist forcetransmit means, wherein the assist motor means is disposed adjacent tothe assist steering system link means.
 8. The steering system of asaddle-ride type vehicle according to claim 7, wherein the assist motormeans is disposed between the steering shaft means and the steering stemmeans in side view.
 9. The steering system of a saddle-ride type vehicleaccording to claim 7, wherein the body frame is connected to a rear endof a swing arm means that extends vehicle forward and rearward and isvertically swingable, wherein a front end of the swing arm means isconnected to a fork holder means for steerably supporting the front forkmeans, and wherein at least a part of the assist motor means overlapswith the swing arm means inside view.
 10. The steering system of asaddle-ride type vehicle according to claim 7, wherein the assist motormeans includes a motor body means and an output shaft means foroutputting rotational drive of the motor body means as the steeringassist force, wherein a steering assist force transmit means is fortransmitting the steering assist force output by the output shaft meansto the steering shaft means, wherein the motor body means is disposeddownward of the steering assist force transmit means, and wherein theoutput shaft means is directed upward.
 11. The steering system of asaddle-ride type vehicle according to claim 10, wherein at least a partof the steering assist force transmit means overlaps with the assiststeering system link means inside view.
 12. The steering system of asaddle-ride type vehicle according to claim 7, further comprising: staymeans for supporting vehicle components, said stay means being attachedto the body frame, wherein the stay means includes an assist motorsupport means for supporting the assist motor means.